Vertical convergence circuit

ABSTRACT

A vertical convergence circuit comprising means for producing a correcting signal having a parabolic waveform in synchronism with vertical scanning, means for separating this correcting signal into two waveforms corresponding solely to the former half and latter half respectively of the vertical scanning period, means for amplifying these two separated correcting signals independently of each other and regulating the amplitude thereof independently of each other, means for inverting the polarity of the two correcting signals independently of each other, and means for applying to the same convergence coil the two correcting signals whose amplitude is regulated and whose polarity is selected by the amplitude regulating means and polarity inverting means.

United States Patent Funakawa et al.

AVAILABLE C [111 [54] VERTICAL CONVERGENCE CIRCUIT 3,767,962 10/1973Arya 315/13 C 7 lnv r Kats F n kawa; z 5] emo S Mats i iinoi m Ryoichi ll ir ta, all of f Exam".1er Maynard wflbur Yokohama Japan AssistantExammer-l M. Potenza Attorney, Agent, or Fzrm-Cratg & Antonelh [73]Assignee: Hitachi, Ltd., Japan- 22 Filed: Apr. 20, 1973 1571 ABSTRACT Avertical convergence circuit comprisin means for [21 Appl. No.. 352,992producing a correcting signal having a par bolic waveform in synchronismwith vertical scanning, means for [30] Foreign Application Priority Dataseparating this correcting signal into two waveforms Apr. 28, 1972 Japan47-42221 Corresponding solely the fume half and latter half respectivelyof the vertical scanning period, means for 1521 us. 01 315/13 camplifying these two Separated correcting Signals inde- 511 lm. c1. H0lj29/70. Pendemly of each other and regulating the amplitude [58] Fidd ofSearch" 315/27 R, 13 C, 13 R, 27 thereof independently of each other,means for invert- 315/370, 371 ing the polarity of the two correctingsignals independently of each other, and means for applying to the [56]References Cited same convergence coil the two correcting signals UNITEDSTATES PATENTS whose amplitude is regulated and whose polarity isselected by the amplitude regulating means and polarity 3,419,74812/1968 Neal et a1 315/13 C inverting means. 3,763,391 10/1973 Rollins315/13 C 3,766,429 10/1973 Vincent et a1. 315/13 C 1 Claim, 9 DrawingFigures SEPARATION REGULATION 33 ml 1. g 3| Tv OUTPUT 4b 6 SEPARATKNOUTPUT PATEHTEDJUL 1 FIG.

v I'LRTICAL CONVERGENCE CIRCUIT Ihis invention relates to a convergencecircuit for use in color tele\ision receivers and more particularly to adynamic convergence circuit for carrying out desll'ckl regulation of theblue electron beam in the vertical direction in a color picture tubehaving three electron guns In a color picture tube such as a shadow masktype color picture tube having a plurality of electron guns. it is knownthat convergence of electron beams of the electron guns throughout thearea of the phosphor screen of the color picture tube is difficult toattain and miscomergence as shown in FIG. I occurs commonly. FIG. Ishows an example of misconvergence occurring at an upper middle portion.central portion and lower middle portion of the screen and thismisconvergence is represented by triangles formed by red. green and bluebeams designated by R. G and B respectively. Desired convergence ofthese three beams can be attained at the central portion of the screenby means of static convergence alignment. However. misconvergcnce shim nin FIG. 1 occurs at the upper middle portion and lower middle portion ofthe screen and the degree of miscomergencc becomes greater at a pointremoter from the center of the screen. Such misconvergenec is shown inan enlarged scale in FIG. 2a. In order to cor rect this misconvergenceby deflecting the beams. the beam spots of the red beam R and green beamG may be transferred to the intersection P of broken lines 1 and 2 alongthese broken lines 1 and 2 respectively and the beam spot of the bluebeam B may be transferred upward in FIG. 2a to attain desiredconvergence. Howewr. due to the fact that generally the beam spots ofthe red beam R and green beam G can only be transferrcd on straightlines along the straight broken lines 1 and 2 shown in FIG. 2a. thedesired convergence of the three beams can only be attained at theintersection P of the straight broken lines 1 and 2. Thus. when thisintersection P is included within a triangle having three ycrtices R. Gand B as shown in FIG. 2a. the beam spot of the blue beam B may betransferred upward in FIG. 2a to attain the desired convergence of thethree beams R. (i and B. It is commonly known that. in order to causesuch transfer of the beam spot of the blue beam B. a correcting currentof parabolic waveform whose period is equal to the vertical scanningperiod T as shown in FIG. 2b may be supplied to the convergence coil forthe blue beam.

In a conventional color picture tube of the kind in which the deflectionangle is less than about 90. the convergence alignment for the blue beamB has been successfully attained by merely transferring the beam spot ofthe blue beam B in one direction since the con icrgencc point P isincluded within a triangle having three \crtices R. G and B as shown inFIG. 2a. Thus. it has been only necessary to supply a correcting currenthaving a waveform as shown in FIG. 2b to the convergcnce coil whilevarying only the magnitude thereof without varying the polarity.However. in the case of a color picture tube of the kind in which thedeflection angle is wide or of the order of 1 a misconvergence triangleas shown in FIG. 3a may be formed by red. green and blue beams R. G andB. In such a case. the beam spot of the blue beam B exists on the screenat a point aboie the convergence point P for the beam spots of the redbeam R and green beam G. and thus;

the beam spot of the blue beam B must be transferred downward in FIG. 3ain the direction opposite to the direction shown in FIG. 2a in order tobring the beam spot of the blue beam B to the point P. In the case ofsuch a triangle. a parabolic correcting current as shown in FIG. 312having a polarity opposite to that shown FIG. 21) must be supplied tothe convergence coil in order to transfer the beam spot of the blue beamB to the point P thereby attaining the desired convergence. It will thusbe seen that. in color picture tubes of wide angle deflection type.there appears the beam triangle of the form shown in FIG. 2a or the beamtriangle of the form shown in FIG. 3a depending on the color picturetube and deflection coils.

It is an object of the present invention to provide a novel and improvedconvergence circuit which is capable of easily and simply attainingconvergence alignment without requiring any especial skill for thecorrection of misconvergence.

Another object of the present invention is to provide a dynamicconvergence circuit for correcting misconvergence in which themisconvergence at an upper portion of the screen of a color picture tubecan be corrected independently of the misconvergence at a lower portionof the tube screen. and the blue beam can be transferred in any desiredvertical direction.

In accordance with the present invention which at tains the aboveobjects. the convergence coil for the blue beam is connected in a bridgecircuit so that the amplitude of the correcting current supplied to theconvergence coil can be continuously varied and the polarity thereof canalso be varied. Further. the parabolic waveform of the correctingcurrent is separated into a waveform corresponding solely to the formerhalf of the vertical scanning period and a waveform corresponding solelyto the latter half of the vertical scanning period and these waveformsare applied to independent amplifiers so that their amplitudes can beregulated independently of each other.

Other objects. features and advantages of the present invention will beapparent from the following detailed description taken in conjunctionwith the accompanying drawings. in which:

FIG. I is a diagrammatic view showing misconvergence triangles formed byred, green and blue beams on the screen of a color picture tube;

FIG. 2a is a schematic enlarged view of a triangle as shown in FIG. 1;

FIG. 2b shows a current waveform required for correcting the blue beamin a misconvergenee tirangle shown in FIG. 211;

FIG. 3a is a schematic enlarged view of another form of the triangle;

FIG. 3b shows a current waveform required for correcting the blue beamin a misconvergence triangle as shown in FIG. 3a;

FIG. 4 is a block diagram of an embodiment of the present invention;

FIG. 5 shows signal waveforms appearing at various parts of FIG. 4; and

FIGS. 6a and 6b are circuit diagrams showing two forms of the practicalcircuitry of the embodiment of the present invention.

The present invention will now be described in detail with reference toFIGS. 4 to 6. FIG. 4 is a basic block diagram of a convergence circuitfor the blue beam according to the present invention, and FIG. 5 showssignal waveforms appearing at various parts of the circuit shown in FIG.4.

Referring to FIG. 4, a parabolic waveform signal whose period is equalto the vertical scanning period is applied to an input terminal 7 of theconvergence circuit. and this signal is applied to a pair of separatingmeans 3a and 3b to be separated into a signal corresponding solely tothe former half of the vertical scanning period and a signalcorresponding solely to the latter half of the vertical scanning periodrespectively. In order to attain the separation of the signal applied tothe separating means 3a and 3b through the input terminal 7, a train ofgate pulses 33 is applied to an input terminal 31 of the separatingmeans 3a and another train of gate pulses 34 is applied to an inputterminal 32 of the separating means 3b. The separating means 3a and 312may be in the form of a switching means which operates in such a mannerthat the input signal appears at the output thereof during the period oftime in which the gate pulse is applied thereto. while such input signaldoes not appear at the output thereof during the period of time in whichno gate pulse appears. These pulse signals 33 and 34 have the samerepetition period as the vertical scanning period T.-. are synchronouswith the vertical scanning and have a duty factor of 50% However. thepulse signal 33 applied to the gate pulse input terminal 31 of theseparating means 30 is 180 out of phase from the pulse signal 34 appliedto the gate pulse input terminal 32 of the separating means 3!). Theparabolic waveform signal corresponding to the former half of thevertical scanning period and the parabolic waveform signal correspondingto the latter half of the vertical scanning period are applied from theseparating means 3a and 3b to respective regulating means 4a and 4bwhich regulate the amplitude of these signals to the level required forcorrection and which can freely invert the polarity of these signals asrequired. These regulating means 4a and 4b are connccted to an outputcircuit 5 to which a convergence coil 6 for the blue beam is connected Aparabolic waveform signal having a repetition period the same as thevertical scanning period T shown by a in FIG. 5 is applied to the inputterminal 7 of the convergence circuit. The signal having such a waveformmay be obtained by applying to an integrating means the sawtoothwaveform signal having the same period as the vertical scanning periodderived from the vertical deflection circuit. This parabolic waveformsignal is separated by the separating means 3a and 3b into a signalcorresponding solely to the former half of the vertical scanning periodas shown by b in FlG. 5 and a signal corresponding solely to the latterhalf of the vertical scanning period as shown by c in FIG. 5. Moreprecisely. the separating means 3a is rendered conductive only duringthe period of time corrcsponding to the former half of the verticalscanning period in response to the application of the pulse signal 33 tothe gate pulse input terminal 31 thereof, and thus. the parabolicwaveform signal applied to the input terminal 7 appears at the output ofthe separating means 30 in the form of an output waveform as shown by bin FIG. 5. Similarly. due to the fact that the pulse signal 34 having aphase opposite to that of the pulse signal 33 is applied to the gatepulse input terminal 32 ot' the separating means 3b. the parabolicwaveform signal applied to the input terminal 7 appears at the output ofthe separating means 312 in the form of an output waveform as shown byin FIG. 5. The two signals corresponding to the former hall and latterhalf ofthc vertical scanning period in this manner are applied toregulating means 4a and 4b respectively in which their amplitude andpolarity are regulated to be suitable for correction. The two signalsthus regulated are applied through the output circuit 5 to theconvergence coil 6 for correcting misconvergence of the blue beam. Oneform of the current waveform flowing through the convergence coil 6 isshown by d in FIG. 5. This example represents the case in which thecorrecting signals appearing from the respective regulating means 4a and4b have different amplitudes to deal with the difference between thedegrees of misconvergence at the upper and lower portions of the screen.In this manner, the amplitude of the correcting signal for the formerhalf of the vertical scanning period can be regulated inde pendently ofthe amplitude of the correcting signal for the latter half of thevertical scanning period. Thus. the convergence alignment can beremarkably facilitated due to the fact that convergence alignment forthe upper portion of the screen can be attained independently of thatfor the lower portion of the screen.

FIG. 6a shows one preferred form of the practical circuitry of theconvergence circuit embodying the present invention. FIG. 6a shows thestages following the separating means 30 and 3b and represents the casein which the regulating means 4a. 4b and the output circuit 5 areunitarily combined. The signal shown by b in FIG. 5 for correcting themisconvergence occurring in the former half of the vertical scanningperiod or the upper portion of the screen is applied to an inputterminal 11. and the signal shown by c in FIG. 5 for correcting themisconvergence occurring in the latter half of the vertical scanningperiod or the lower half of the screen is applied to another inputterminal 12. These signals are applied to the base of respectiveamplifying transistors 13 and 14 which are connected at the collcctorthereof to a bias voltage applying terminal 10. A pair of variableresistors 15 and 16 are provided for regulating the amplitude andpolarity of the correcting current supplied to a convergence coil 61 forthe blue beam. A capacitor is connected between ground and the emitterof each of the transistors 13 and 14 so as to prevent damage to thetransistors 13 and 14 due to direct application of a high voltage whichmay be induced in the convergence coil 61 and leads therefor due to aspark. A pair of fixed resistors 17 and 13 constitute a bridge circuittogether with the variable resistors 15 and 16 so that the direction andamplitude of the correcting current flowing through the convergence coil61 can be varied depending on the position of the sliding terminal ofthe variable resistor 15 or 16. When the sliding terminal of thevariable resistor 15 (or 16) is in its intermediate position such thatthe resistances of the left-hand and right-hand portions of the resistorare equal to each other, the current from the transistor 13 (or 14) isnot supplied to the convergence coil 61. As the sliding terminal movesin either direc' tion from this neutral point. the current flows throughthe convergence coil 61 in one direction or the other depending on themoving direction of the sliding terminal. and the amplitude of thecurrent is increased as the liding terminal approaches either extremity.

As described above. the parabolic correcting voltage is separated intotwo portions for correcting the misconvergence occurring in the formerhalf and latter half of the vertical scanning period and such voltagesare applied to the base of the respective transistors 13 and 14. Forexample a voltage having a waveform as shown by b in FIG. 5 is appliedto the base of the transistor l3 and a voltage having a waveform asshown by L' in FIG. 5 is applied to the base of the transistor 14. Thus,when the transistor 13 is conducting. the transistor 14 is cut off whilewhen the transistor 14 is conducting. the transistor 13 is cut off.Therefore. the emitter current of the transistors 13 and 14 flowsalternately through the convergence coil 61. Since the amplitude anddirection of the emitter current of the transistor 13 can be selectedindependently of those of the emitter current of the transistor 14 bymanipulating the variable resistors 15 and 16, the desired convergencealignment can be easily and simply attained even when the degree ofmisconvergence at the upper portion of the screen differs from that atthe lower portion of the screen. ln an extreme case, the direction ofthe misconvergence correcting current for the upper portion of thescreen can be reversed relative to the direction of such current for thelower portion of the screen.

FIG. 6b shows another preferred form of the practical circuitry of theconvergence circuit embodying the present invention, and the stagesfollowing the separatmg means 3a and 3b are also merely shown as in FIG.but The signal for correcting the misconvergence occurring in the formerhalf of the vertical scanning period is applied to an input terminal 21,and the signal for correcting the misconvergence occurring in the lattcrhalf of the vertical scanning period is applied to another inputtcrminal 22. A pair of variable resistors 25 and 26 are similarlyprovided for regulating the amplitude and polarity of these correctingsignals. A pair of transistors 23 and 24 act to amplify the correctingsignals and are connected at the collector thereof to a bias voltageapplying terminal 20. A convergence coil 62 for the blue beam isconnected across the collectors of the transistors 23 and 24.

The operation of the circuit shown in H6. 6/; is basically entirely thesame as that of the circuit shown in FIG. 6a except that the amplitudeand polarity of the correcting signals are first regulated and then thecorrecting signals are amplified to be applied to the con vergence coil62.

It will be understood from the foregoing detailed de scription thatconvergence alignment can be remarkably easily and simply attainedaccording to the present invention by virtue of the fact that the beamspot of the electron beam for providing the blue color can betransferred in any desired vertical direction and the misconvergenceoccurring at the upper portion of the screen and the misconvergenceoccurring at the lower portion of the screen can be correctedindependently of each other.

What is claimed is:

l. A dynamic vertical convergence circuit comprising means for producinga signal for correcting misconvergence, said signal being synchronouswith the vertical scanning and having the same repetition period as thevertical scanning period; means for separating said correcting signalinto a first half signal having a waver form corresponding solely to theformer half of the vertical scanning period and a second half signalhaving a waveform corresponding solely to the latter half of thevertical scanning period; a first transistor having a base supplied withsaid first half signal, a collector connected to a power supply source,and an emitter; a second transistor having a base supplied with saidsecond half signal, a collector connected to said power supply source,and an emitter; a first variable resistor having a sliding terminal; asecond variable resistor having a sliding terminal and connected inparallel with said first variable resistor; a first fixed resistorconnected between a point of a reference potential and one of theconnecting points of said first and second variable resistors; a secondfixed resistor connected between a point of a reference potential andthe other connecting point of said first and second variable resistors;a convergence coil connected in parallel with said first and secondvariable resistors; means for connecting the emitter of said firsttransistor directly to said sliding terminal of said first variableresistor so that said second half signal does not cause conductionbetween said emitter of said first transistor and said referencepotential; and means for connecting the emitter of said secondtransistor directly to said sliding terminal of said second variableresistor so that said first half signal does not cause conductionbetween said emitter of said second transistor and said referencepotential; whereby the amplitude and polarity of said first and secondhalf signals supplied from the respective sliding terminals of saidfirst and second variable resistors to said convergence coil can beregulated independently of each other by suitably sliding the slidingterminals of said first and second variable resistors.

1. A dynamic vertical convergence circuit comprising means for producinga signal for correcting misconvergence, said signal being synchronouswith the vertical scanning and having the same repetition period as thevertical scanning period; means for separating said correcting signalinto a first half signal having a wave-form corresponding solely to theformer half of the vertical scanning period and a second half signalhaving a waveform corresponding solely to the latter half of thevertical scanning period; a first transistor having a base supplied withsaid first half signal, a collector connected to a power supply source,and an emitter; a second transistor having a base supplied with saidsecond half signal, a collector connected to said power supply source,and an emitter; a first variable resistor having a sliding terminal; asecond variable resistor having a sliding terminal and connected inparallel with said first variable resistor; a first fixed resistorconnected between a point of a reference potential and one of theconnecting points of said first and second variable resistors; a secondfixed resistor connected between a point of a reference potential andthe other connecting point of said first and second vaRiable resistors;a convergence coil connected in parallel with said first and secondvariable resistors; means for connecting the emitter of said firsttransistor directly to said sliding terminal of said first variableresistor so that said second half signal does not cause conductionbetween said emitter of said first transistor and said referencepotential; and means for connecting the emitter of said secondtransistor directly to said sliding terminal of said second variableresistor so that said first half signal does not cause conductionbetween said emitter of said second transistor and said referencepotential; whereby the amplitude and polarity of said first and secondhalf signals supplied from the respective sliding terminals of saidfirst and second variable resistors to said convergence coil can beregulated independently of each other by suitably sliding the slidingterminals of said first and second variable resistors.